Soybean rust (SBR) was detected on July 31st in a commercial soybean field near Rohwer in Desha County Arkansas. This is the first report of SBR this year in the state, which is about one week earlier than 2009, the last time it was reported in Arkansas. Currently, this is the farthest north SBR has been confirmed this year in the U.S. The disease severity was low with an average of five pustules per leaflet, and disease incidence was extremely low in this field. Infected leaves were located in the lower canopy. Soybeans were at growth stage R7. It is likely to find other small pockets of SBR in counties that neighbor Desha; however, there is a low risk of disease progression due to drought conditions that cover much of the state and with the forecast for hot, dry weather. Based on climatic weather conditions, it is unlikely for SBR to be as widespread or severe as compared to the 2009 growing season when conditions were more favorable for disease development. Producers and consultants in the southeastern part of the state are encouraged to monitor fields along the Mississippi River for SBR before applying a fungicide. The purpose of this report is to extend to producers that SBR has been found in AR, but it is not a time for widespread application of fungicides. We will continue to monitor sentinel plots and investigate commercial fields in Southeast AR and across the state.
There was no recommendation for a fungicide to be applied on this field because it would NOT contribute to an economical gain in yield and rust was NOT actively producing spores. Conditions needed for this infection probably occurred earlier in July when rain fell over the southeastern part of the state. General recommendations for fungicide applications for SBR were posted last week on this blog. For a quick summary, the first application should be made from R1 to R3 for high-risk fields where rust threatens and at R1 if rust has been observed in the local area. Based on our last trip through the southeastern part of the state, most of the beans are past this stage of growth. There is no recommendation to spray at R6 growth stage or later. Finally, there is no recommendation for widespread application of fungicides to manage SBR at this time, rather monitor field for SBR prior to any fungicide application. Future updates will be posted on this blog and IPM-PIPE.